1. Field of the Invention
This invention relates to a thermoforming method and apparatus for making a bowl-shaped container out of a thermoplastic resin sheet, a thermoforming female die, a method of thermoforming a bowl-shaped container, a thermoforming plug, a method of thermoforming a product with undercut and a thermoforming female die.
2. Description of the Prior Art
When a bowl-shaped container having a rim of a bottom is made of a thermoplastic resin sheet, the melted resin sheet is conventionally folded at the rim of the bottom. FIG. 21 shows a section of the rim made in this conventional method. Also, when a body of the container is rendered rugged, the thermoplastic resin sheet is folded into folds. FIG. 22 shows a section of the rugged body.
Japanese Patent Publication Nos. 50-87162A and 50-67370A disclose adjustment of thickness in the thermoforming by a plug. In the former, the plug is formed to be circumferentially split and each of split pieces is pivotally supported on an outer circumferential side of a base so that the diameter of an upper outer circumferential end can be spread and reduced. The plug in the reduced state is caused to abut against the thermoplastic resin sheet so that the sheet is pushed into a female die. Thereafter, the diameter of the plug is spread. This changes the degree of preliminary extension of a bottom wall of the thermoformed product, whereby the thickness is adjusted.
In the latter, the plug is supported on an elastic member such as a coil spring. While abutted against a thermoplastic resin plate, the plug is caused to strike against the female die so that the spring is contracted. As a result, the preliminary extension is carried out by the stroke of the spring in addition to the length of the plug regarding the circumferential wall.
In the thermoforming, the thermoplastic resin plate is heated so as to be plastic and then sucked into a die for the forming. The thermoplastic resin plate is thereafter removed from the die. Since the thermoplastic resin plate, even when hardened, has flexibility, a certain undercut can be performed.
In the aforesaid conventional method, an annular opening is formed in the bottom of the folded container so as to correspond to the rim. Accordingly, when poured into the container, soup or the like enters the annular opening. This results in no problem when the container is non-returnable. However, when the container is cleaned for re-use, it is difficult to wash away the soup or the like remaining in the annular opening. It is also difficult to wash away the soup or the like remaining in openings of the folds formed in the body of the container.
Further, the aforesaid thermoforming plugs have the following problems. Since the plug is split and pivoted in the former, the construction thereof becomes complicated. In the latter, the plug is caused to abut against the inner face of the female die. At this time, the thickness is reduced and accordingly, the plug cannot actually be employed.
Further, in the conventional method of thermoforming the product with an undercut, an allowed undercut is small. For example, when a rim of a bottom is made as a bowl for cupped noodle, a satisfactory result cannot be achieved.
Therefore, an object of the present invention is to provide a thermoforming apparatus and method, a thermoforming femele die, and a method of thermoforming a bowl-shaped container, which form the bowl-shaped container by folding a part of the resin sheet and yet which can prevent soup or the like from entering the opening formed in the bottom or the body thereof, a thermoforming plug, termoforming apparatus and method, which can provide a flexible thickness adjustment with a simple construction, a method of thermoforming a molding with an undercut and a thermoforming female die therefore, which can allow a large undercut to be stably removed from the die.
To accomplish the object, a first embodiment of the invention provides a thermoforming apparatus compressing a thermoforming female die and a plug moved forward and backward so that a softening thermoplastic resin sheet is thrust into the thermoforming female die. In the apparatus, the thermoforming female die includes a rim forming recess formed generally into a shape of a bowl-shaped recess, communicating with a bottom opening and of the bowl, an outer wall, a bottom wall and an inner wall of a rim of the bottom, and a bottom plate formed into a columnar shape similar to the bottom opening and supported to be moved forward and backward relative to the rim forming recess, the bottom wall being driven between a first position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the bottom opening. Further, the thermoplastic resin sheet heated to be softened is thrust by the plug while the bottom plate is held at the first stop position. The thermoplastic resin sheet is brought into close contact with an inner circumferential surface of the bowl-shaped recess and immediately thereafter, the bottom plate is moved to the second stop position so that a rim is formed.
In the invention of the first embodiment thus constructed, the thermoforming apparatus the thermoforming female die and the plug moved forward and backward so as to thrust the thermoplastic resin sheet into the thermoforming female die. The thermoforming female die is formed into a generally bowl-shaped recess. The female die has the rim forming recess communicating with a bowl bottom opening of the bowl-shaped recess so as to form the bottom wall of the bowl-shape and an outer form wall, bottom wall and inner wall of the rim. The bottom plate formed into the columnar shape similar to the bottom opening is supported to be moved forward and backward relative to the rim forming recess. The bottom plate is driven between the first stop position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the bottom opening.
Accordingly, the thermoplastic resin sheet heated to be softened is thrust by the plug into the female die while the bottom plate is held at the first stop position. When brought into close contact with the inner circumferential surface of the bowl-shaped recess, the thermoplastic resin sheet is expanded along the top of the bottom plate located inside the rim forming recess. However, immediately thereafter, the bottom plate is moved to the second stop position. Accordingly, the thermoplastic resin sheet on the top of the bottom plate is pushed up from the rim forming recess side to the bottom opening of the bowl-shaped recess. Then, a peripheral edge of the thermoplastic resin sheet turned up by the bottom plate and a part of the sheet positioned in the vicinity of the opening of the rim forming recess are welded together. More specifically, although the part of the sheet in the rim forming recess is expanded, the bowl bottom is immediately moved upward toward the bottom opening so that the parts of the sheet are welded together.
According to the first embodiment of the invention, when the bowl-shaped container with a rim is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
A second embodiment of the invention is constructed so that in the thermoforming apparatus of the first embodiment, the rim forming recess includes a first portion spread outward so as to be continuous from the bowl bottom and a second portion continuous from the first portion and having a reduced inner diameter, the first and second portions forming the outer wall and the bottom wall.
In the invention of the second embodiment thus constructed, the rim forming recess is spread out from the bowl bottom opening and its inner diameter is then reduced. Accordingly, a spread rim outer side wall surface is formed by this inclined portion. Further, a bottom wall of the rim is formed by a flat portion where the inner diameter is reduced. Additionally, the rim inner wall surface turned up to be welded is welded in the bowl bottom opening such that the rim forming recess has a generally triangular section and a cavity is formed inside the rim.
According to the second embodiment of the invention, the outer form of the rim is spread out such that a high-quality bowl-shaped container having stability and voluminousness can be made. A third embodiment of the invention is constructed so that in the thermoforming apparatus of the first embodiment, the rim forming recess includes a first portion continuous from the bottom opening with a diameter thereof maintained substantially at the same value and a second portion continuous from the first portion and having a reduced inner diameter, the first and second portions forming the outer wall and the bottom wall.
In the third embodiment of the invention thus constructed, a vertical outer form of the rim is formed by a portion of the rim forming recess continuous from bowl bottom opening with the diameter being maintained at the same value. An inner circumferential surface of the rim is formed by turning up a portion of the sheet continuous from a portion with a slightly reduced inner diameter. The thermoplastic resin sheet is reversed at a portion where both portions are continuous. The reversed portion forms a bottom wall. In this case, a rim outer side wall surface and a rim inner side wall surface are welded together such that the rim becomes solid.
According to the third embodiment of the invention, a strong rim can be formed by superposing two thermoplastic resin sheets.
A fourth embodiment of the invention is constructed so that in the thermoforming apparatus of the third embodiment of the invention, the second portion of the rim forming recess has a thickness slightly smaller than a doubled thickness of the thermoplastic resin sheet such that the thermoplastic resin sheet is prevented from being turned up when folded back.
In the fourth embodiment of the invention thus constructed, the rim forming recess has a concentric cylindrical portion. The portion with the reduced inner diameter is pushed up by ascend of the bottom plate, so that the portion is revered to a side with a large inner diameter. Since the clearance in which the thermoplastic resin sheet is folded has a thickness substantially equal to a double of the thickness of the thermoplastic resin sheet, two sheets are superposed to be welded together, pushed against each other. Accordingly, the slightly narrow range is set so as to meet such conditions. Since the thermoplastic resin sheet is expanded by the plug, the sheet becomes thinner as compared with the original thickness. On the basis of this, the second and subsequent sheets are slightly narrowed.
According to the fourth embodiment of the invention, the sheet can accurately be folded back without turning up the outer wall when the rim is formed.
A fifth embodiment of the invention is constructed so that in the thermoforming apparatus of any of the first four embodiments, the rim forming recess extends inward substantially by a length of the rim from the first and second portions forming the outer wall and the bottom wall.
In the fifth embodiment of the invention thus constructed, the thermoplastic resin sheet is continuous inward substantially by the length of the rim. Accordingly, the thermoplastic resin sheet is once expanded more than the bottom wall and thereafter, this portion is folded to be formed into a rim inner side wall surface. That is, since the thermoplastic resin sheet is expanded by an amount corresponding to a folded portion, the rim outer side wall surface can be prevented from being turned up when the sheet is folded.
According to the fifth embodiment of the invention, since a folding portion is previously ensured, the inside wall face can accurately be folded back.
A sixth embodiment of the invention is constructed so that in the thermoforming apparatus of any one of the first five embodiments, the thermoforming female die has a heater disposed near the rim forming recess so that a temperature near the rim forming recess is higher than a temperature in the other portion.
In the sixth embodiment of the invention thus constructed, the heater is disposed near the rim forming recess in the thermoforming female die and accordingly, the temperature of this portion can be increased as compared with the other portion. Since the temperature is high, the thermoplastic resin sheet is not immediately hardened even when coming into contact with the inner circumferential surface of the rim forming recess. The thermoplastic resin sheet is turned up in the half-melted state at the time the bottom plate is driven. The ordinary hardening starts some time after the sheet has been turned up. That is, increasing the temperature retards hardening and accordingly, the temperature is not increased to such a value as to melt the sheet.
According to the sixth embodiment of the invention, the thermoplastic resin sheet can be prevented from hardening immediately at an initial stage of the forming.
The thermoforming apparatus of the present invention is mainly characterized by the female die and the invention may be constructed as the sole invention of the thermoforming female die. Thus, a seventh embodiment of the invention is a thermoforming female die including a rim forming recess formed generally into a shape of a bowl-shaped recess, communicating with a bottom opening and forming a bottom wall of the bowl, an outer wall, a bottom wall and an inner wall of a rim of the bottom, and a bottom plate formed into a columnar shape similar to the bottom opening and supported to be moved forward and backward relative to the rim forming recess, the bottom wall being driven between a first stop position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the bottom opening.
According to the seventh embodiment of the invention, when the bowl-shaped container with a rim is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
Further, the invention may be constructed as a method of forming the rim. Thus, an eighth embodiment of the invention is a method of thermoforming comprising the steps of communicating a rim forming recess formed generally into a shape of a bowl-shaped recess with a bottom opening and forming a bottom wall of the bowl, an outer wall, a bottom wall and an inner wall of a rim of the bottom, supporting a bottom plate inside the rim forming recess so that the bottom plate is moved forward and rear ward relative to the rim forming recess, the bottom plate being formed into a columnar shape similar to the bottom opening so that the bottom plate is moved forward and backward relative to the rim forming recess, bringing the thermoplastic resin sheet heated to be softened into close contact with an inner circumferential surface of the bowl-shaped recess and immediately thereafter, moving the bottom plate to the second stop position so that a rim is formed, and retreating the bottom plate to the first stop position.
According to the eighth embodiment of the invention, when the bowl-shaped container with a rim is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
Further, the invention may be constructed as a method of making a bowl-shaped container with a rim. Thus, a ninth embodiment of the invention is a method of thermoforming a bowl-shaped container in which a thermoplastic resin sheet heated to be softened is brought into close contact with an inner circumferential surface of thermoforming female die formed generally into a bowl shaped recess, the method comprising the steps of communicating a rim forming recess formed generally into a shape of a bowl-shaped recess with a bottom opening and forming a bottom wall of the bowl, an outer wall, a bottom wall and an inner wall of a rim of the bottom, supporting a bottom plate inside the rim forming recess so that the bottom plate is moved forward and rear ward relative to the rim forming recess, the bottom plate being formed into a columnar shape similar to the bottom opening so that the bottom plate is moved forward and backward relative to the rim forming recess, bringing the thermoplastic resin sheet heated to be softened into close contact with an inner circumferential surface of the bowl-shaped recess and immediately thereafter, moving the bottom plate to the second stop position so that a rim is formed, and retreating the bottom plate to the first stop position.
According to the ninth embodiment of the invention, when the bowl-shaped container with a rim is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
A tenth embodiment of the invention is a thermoforming apparatus which includes a thermoforming female die unit and a plug unit, wherein the thermoforming female die unit includes a main die formed generally into a bowl-shaped recess and having a body formed with a number of grooves, the plug unit includes a plug thrusting a softening thermoplastic resin sheet into the main die in a primary forming, a male die pressed against a portion of an inner circumferential surface corresponding to positions of the grooves after the primary forming while a primary product is held in the main die, and a switching mechanism for switching the plug and the male die.
In the tenth embodiment of the invention thus constructed, a number of grooves are formed in the body of the main die formed generally into a bowl-shaped recess. When the softening thermoplastic resin sheet is pushed into the grooves by the plug of the plug unit in a primary forming to be brought into contact with the inner circumferential surface, the sheet enters the grooves such that the sheet assumes such a state as to be folded back. At this time, however, the resin sheet is only folded and gaps are formed. Accordingly, the plug is switched to the male die by the switching mechanism to be pushed into the main die in the state where the primary molding is held in the main die after the primary forming. The male die has such a form as to be pressed against locations of the grooves in the main die, whereby the same effect is achieved as a part of the sheet out of the grooves in the main die is pressurized to be forced into the grooves. As a result, present gaps are closed.
According to the tenth embodiment of the invention, when the bowl-shaped container with a number of ribs on the body thereof is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
The thermoplastic resin sheet is pushed into the grooves with the male die. However, it is effective that the thermoplastic resin sheet is rendered easy to be pushed into the grooves. For this purpose, an eleventh embodiment of the invention is constructed so that in the thermoforming apparatus of the tenth embodiment of the invention, the main die has a heater for heating the body formed with the grooves.
In the eleventh embodiment of the invention thus constructed, the temperature of the body formed with the grooves can be increased. Accordingly, the thermoplastic resin sheet can be prevented from being hardened before being pushed into the grooves and can easily be pushed into the grooves.
According to the eleventh embodiment of the invention, the ribs can be prevented from hardening immediately at an initial stage of the thermoforming.
When a heater is provided, it is worthwhile to use a cooling male die for cooling so that the sheet becomes easy to be hardened. In order that a part of the main die may be heated, a twelfth embodiment of the invention is constructed so that in the thermoforming apparatus of the eleventh embodiment, the main die includes an independent die constituting a portion thereof in which the heater is provided.
In the twelfth embodiment of the invention thus constructed, the portion of the main die having the heater is formed as an independent die. Accordingly, heat is difficult to transfer to the other portion and a suitable temperature control can be provided.
According to the twelfth embodiment of the invention, the temperature of a necessary portion can efficiently be controlled.
The thermoforming apparatus of the present invention is mainly characterized by the female die and the invention may be constructed as the sole invention of the thermoforming female die. Thus, a thirteenth embodiment of the invention is a thermoforming female die formed generally into a shape of a bowl-shaped recess and including one portion which forms a body and is constituted by another die independent of the other portion thereof, wherein said one portion is provided with a heater and has a number of grooves formed in an inner circumferential surface thereof, wherein a softening thermoplastic resin sheet is thrust by a plug into the die in a primary forming, and wherein while a primary product is held in the die, the plug is switched to a cooling male die after the primary forming so that the cooling male die is pressed against a portion of the inner circumferential surface of the die where the grooves are formed so that ribs are formed on the grooves.
According to the thirteenth embodiment of the invention, when the bowl-shaped container with a number of ribs on the body thereof is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
Further, the invention may be constructed as a making a rib. Thus, a fourteenth embodiment of the invention is a thermoforming method comprising the steps of forming a number of grooves in a body of a main die of a thermoforming female die unit, the main die being formed generally into a shape of a bowl-shaped recess, thrusting a softening thermoplastic resin sheet into the main die by a plug in a primary forming, and switching the plug to a male die after the primary forming while a primary product is held in the main die, thereby pressing the mail die against a portion of the inner circumferential surface of the die where the grooves are formed so that ribs are formed on the grooves.
According to the fourteenth embodiment of the invention, when the bowl-shaped container with a number of ribs on the body thereof is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
Further, the invention may be constructed as a making a bowl-shaped container with such a rib. Thus, a fifteenth embodiment of the invention is a method of thermoforming a bowl-shaped container in which a softening thermoplastic resin sheet is interposed between a thermoforming female unit and a plug unit and a bowl-shaped container is made out of the sheet by thermoforming, the method comprising the steps of forming a number of grooves in a body of a main die of the thermoforming female die unit, the main die being formed generally into a shape of a bowl-shaped recess, thrusting a softening thermoplastic resin sheet into the main die by a plug in a primary forming, and switching the plug to a male die after the primary forming while a primary product is held in the main die, thereby pressing the mail die against a portion of the inner circumferential surface of the die where the grooves are formed so that a bowl-shaped container with ribs at locations corresponding to the body.
According to the fifteenth embodiment of the invention, when the bowl-shaped container with a number of ribs on the body thereof is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
Further, in order that a flexible thickness adjustment may be carried out by a simple construction, the sixteenth embodiment of the invention is a thermoforming plug comprising a plug body and a sub plug accommodated in the plug body and moved forward and backward to and from a female die to thereby assist a thickness adjustment.
In the sixteenth embodiment of the invention thus constructed, the sub plug is accommodated in the plug body so as to be moved forward and backward to the interior of the female die. Generally, the thickness of the molding is increased as the gap between the inner circumferential surface of the female die and the plug comes near, whereas the thickness is reduced as the gap is departed away. Accordingly, the sub plug is caused to protrude in a portion whose thickness is to be increased.
According to the sixteenth embodiment of the invention, partial thickness adjustment can easily be assisted by the construction in which the sub plug is moved forward and backward from the plug body.
In what part of the plug body the sub plug should be accommodated is determined according to the requirement of the thickness adjustment. As one example, a seventeenth embodiment of the invention is constructed so that in the thermoforming plug of the sixteenth embodiment of the intention, the plug body and the sub plug are substantially concentric.
In the seventeenth embodiment of the invention thus constructed, an area of the top of the plug is variable as the sub plug is moved forward and backward when the plug body and the sub plug are concentric. More specifically, the area of the top is equal to an area of the plug body when the sub plug does not project. The area of the top is equal to an area of the sub plug when the latter projects. Further, the distance to the circumferential surface of the female die changes depending upon whether the sub plug projects. These elements work as a whole so that a partial adjustment of the thickness is carried out.
According to the seventeenth embodiment of the invention, the thickness can be adjusted by the changes in the bottom area and distance.
Of course, both of them need not be accurately concentric. Roughly the sub plug may only be moved forward and backward from the inside of the top of the plug body.
Various conventional constructions for moving the sub plug forward and backward may be employed. As one suitable example, an eighteenth embodiment of the invention is constructed so that in the thermoforming plug of the sixteenth or seventeenth embodiment of the invention, the sub plug is accommodated and supported in the plug body and communicates with an airtight chamber inside the plug body so as to be moved forward and backward according to a pressure difference between the airtight chamber and an exterior.
In the eighteenth embodiment of the invention thus constructed, the airtight chamber is formed inside the plug body, and the sub plug is accommodated in the plug body so as to communicate with the airtight chamber. Accordingly, the pressure adjustment is carried out between the airtight chamber and the exterior so that the sub plug is moved forward and backward. For example, when the negative pressure is applied to the sub plug while the exterior is maintained at a predetermined pressure, the sub plug is accommodated into the plug body. The sub plug projects when compressed air is supplied into the airtight chamber. As well known, the pressure outside the plug body is controlled and the pressure difference is adjusted to the extent required for the driving control of the sub plug. More specifically, the sub plug projects when the pressure higher than in the exterior is supplied to the airtight chamber. The sub plug is accommodated into the plug body when the airtight chamber is opened to the atmosphere in the above-described state.
According to the eighteenth embodiment of the invention, the drive of the sub plug is controlled only by the pressure difference. As a result, the construction of the plug and the forming timing can be simplified.
Thus, when the forward and backward movement of the sub plug is controlled by the pressure difference, various structures for supporting the sub plug can be proposed. As one example, a nineteenth embodiment of the invention is constructed so that in the thermoforming plug of the eighteenth embodiment of the invention, the plug body and the sub plug are formed into shapes of a cylinder and a piston respectively.
In the nineteenth embodiment of the invention thus constructed, the sub plug and the plug body have a structure of a piston and a cylinder. Since the sub plug is accommodated and supported in the cylindrical portion formed in the plug body, the pressure is adjusted between the airtight chamber inside the plug body and the exterior so that the sub plug can be moved forward and backward in the form of a piston.
According to the nineteenth embodiment of the invention, the sub plug and the plug body has a simplified construction as that of the cylinder and piston.
The aforesaid thermoforming plug is not used independently but used as a part of the thermoforming apparatus. The thickness adjustment can be desirably carried out in the thermoforming apparatus. In this meaning, a twentieth embodiment of the invention is a method of thermoforming a product in which a plug is moved forward and backward into and out of a thermoforming female die so that a softening thermoplastic resin plate is preliminary extended, thereby thermoforming a product, wherein the plug includes a plug body and a sub plug accommodated in the plug body and moved forward and backward to and from the female die, the method comprising the steps of putting the plug body and the sub plug into the thermoforming female die with the sub plug projecting, and retreating the sub plug thereafter so that a thickness adjustment is carried out.
In the twentieth embodiment of the invention thus constructed, the plug body and the sub plug are caused to enter the thermoforming female die with the sub plug projecting. Accordingly, the distance to the inner circumferential surface of the female die is small and the thickness is increased in the vicinity of the inner circumferential surface. Further, since the sub plug is thereafter moved backward, drawbacks due to the shortened gap between the inner circumferential surface of the female die and the plug can be avoided.
According to the twentieth embodiment of the invention, the thickness adjustment can easily be carried out.
Of course, the thickness adjustment has merits even if such drawbacks do not occur. However, the above-described method is suitable for a case where the drawbacks need to be solved. As one example, a twenty-first embodiment of the invention is a thermoforming apparatus comprising a thermoforming female die and a plug moved forward and backward so that a softening thermoplastic resin plate is thrust into the thermoforming female die, wherein the thermoforming female die includes a rim outer shape recess formed into a shape of a bowl-shaped recess and forming a rim outer peripheral shape spread outward so as to be continuous from the bowl bottom, and a rim inside forming die formed into a columnar shape similar to an open edge of the rim outer shape recess continuous to the bowl-shaped recess and supported to be moved forward and backward relative to the bowl-shaped recess, the rim inside forming die being driven between a first stop position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the open edge, and the plug includes a plug body allowed to enter the bowl-shaped recess and a sub plug formed into such a columnar shaped as to enter an opening of the rim outer shape recess and supported so as to be moved forward and backward relative to the bowl-shaped recess, the sub plug being reciprocated without abutting against rim inside forming die when the rim inside forming die is reciprocated between the first and second stop positions.
In the twenty-first embodiment of the invention thus constructed, a spread-out rim is formed by the bowl bottom of the thermoforming female die formed into the bowl-shaped recess. Accordingly, the spread-out rim outer form recess is formed which is continuous from the bowl bottom of the bowl-shaped recess. The columnar rim inside forming die, which is similar to an open edge to the bowl-shaped recess, is accommodated in the bowl bottom of the bowl-shaped recess so as to be moved forward and backward. The rim inside forming die is moved between the first stop position where the bottom plate is retreated inside the rim forming recess and the second stop position where the bottom plate is in the vicinity of the open edge. The rim inside forming die is on standby at the first stop position at the time of start of the forming. Accordingly, the softened thermoplastic resin plate needs to be drawn from the bowl bottom of the bowl-shaped recess through the rim outside recess to the rim inside forming die.
According to the twenty-first embodiment of the invention, a rim having an increased thickness can be formed.
In this case, the conventional plug cannot push the thermoplastic resin plate inside the bowl bottom of the female die. This results in an increase in the distance from the plug to the rim outside forming recess or the rim inside forming die. However, the above-described plug includes the plug body moved into the bowl-shaped recess and the columnar sub plug moved into the opening of the rim outside forming recess. The sub plug projects so that the thermoplastic resin plate is thrust into the position near the rim outside forming recess or the rim inside forming die. The rim inside forming die is supported to be moved forward and backward in order that the thermoplastic resin plate drawn inside the bowl bottom may be returned to the opening side so that the rim is formed by the rim outside forming recess spread-out from the opening edge and the bowl bottom continuous from the bowl-shaped recess without any large stepped portion. Since the rim inside forming die is moved from the first stop position to the second stop position, the sub plug interferes with the molding when the sub plug projects. Further, the thickness cannot be increased when such a distance as not to result in interference is provided.
Consequently, the rim inside forming die can be reciprocated between first and second stop positions such that the sub plug can be reciprocated without contact, whereby the thickness can be increased to the maximum. Further, in order that even a large undercut can stably be released from a die and made, a twenty-second embodiment of the invention is a method of thermoforming a product with an undercut wherein vacuum and die-releasing holes are concentrically provided in an undercut forming portion of a thermoforming die, comprising the step of supplying compressed air through the vacuum and die-releasing holes during die-release so that an undercut portion of the product is flexed, thereby assisting the die-release from the undercut forming portion.
In the twenty-second embodiment of the invention thus constructed, the thermoforming die includes an undercut forming portion, and the vacuum and die-releasing holes are formed concentrically in the vicinity of the undercut forming portion. Accordingly, when compressed air is supplied from the vacuum and die-releasing holes during the die-releasing, the undercut-shaped portion of the molding is flexed, whereupon a superposed portion with respect to the undercut forming portion is increased such that the undercut-shaped portion is easy to be removed. According to the twenty-second embodiment of the invention, a larger undercut can stably be removed from the die.
The thermoforming die may basically comprise either male die or female die. As one example, a twenty-third embodiment of the invention is constructed so that in the method of the twenty-third embodiment of the invention, the thermoforming die comprises a female die having a shape of a bowl-shaped recess, wherein the undercut forming portion is spread out from a bowl bottom of the bowl-shaped recess inward, and wherein the compressed air is supplied through the vacuum and die-releasing holes so that the bottom of the product is flexed, thereby assisting the die-release from the undercut forming portion.
In the twenty-third embodiment of the invention thus constructed, the thermoforming die is a female die having the bowl-shaped recess and is formed so as to be spread out inward from the bowl bottom of the recess. Accordingly, when the molding is drawn out of the female die, the spread-out portion becomes an undercut. Since the vacuum and die-releasing holes are formed concentrically in the vicinity of the undercut forming portion, pressure is applied from the outside to the inside of the bowl bottom when compressed air is supplied by the vacuum and die-releasing holes during the die-releasing. When the pressure is applied from the bowl bottom side, the bowl bottom is flexed inward about the portion farthest from the opening end. Then, a projecting portion spread out from the bowl bottom is inclined relative to the undercut forming recess provided in the female die and can easily pass through the recess. According to the twenty-third embodiment of the invention, a form spread out inward from the bowl bottom can be obtained.
When the undercut is formed on the bowl bottom and the vacuum and die-releasing holes are concentrated onto the portion near the undercut, no holes are disposed in the side near the opening end. As a result, the thermoplastic resin plate tends to be brought into contact with the inner circumferential wall surface of the die in a portion at the opening end side. In view of this, a twenty-fourth embodiment of the invention is constructed so that in the method of the twenty-third embodiment of the invention, the vacuum and die-releasing holes are formed in the female die, wherein a hole communicating with atmosphere is formed in a portion of the bowl-shaped recess in the vicinity of an open end, and wherein compressed air is supplied through the inside of the product during the forming.
In the twenty-fourth embodiment of the invention thus constructed, the hole communicating with the atmosphere is formed in the portion in the vicinity of the open end. Compressed air is supplied through the inside of the bowl during the forming. The vacuum and die-releasing holes are formed in the bowl bottom side. When the negative pressure is applied to the holes during the forming, air is sucked along the inner circumferential surface of the forming die. On the other hand, since compressed air is supplied from the bowl inside of the molding during the forming a portion near the opening end is pressed against the inner circumferential surface of the forming die as well as the bowl bottom. Air between both of them is sucked through a suction hole at the bowl bottom side and is exhausted through the hole communicating with the atmosphere at the opening end side.
According to the twenty-fourth embodiment of the invention, the portion near the opening end of the bowl-shaped recess can be formed into a desired shape even if the vacuum and die releasing holes are formed concentrically in the bowl bottom.
Synchronizing the supply of compressed air with another operation is effective. As one example, a twenty-fifth embodiment of the invention is constructed so that in the method of any one of the twenty-second to twenty-fourth embodiments, supply of compressed air through the vacuum and die-releasing holes is initiated before knock-out.
In the twenty-fifth embodiment of the invention thus constructed, since the compressed air is supplied prior to the knockout, the supply of compressed air starts when a portion near the opening end is adherent on the die, whereupon the bowl bottom tends to be flexed. The reason for this is that even when compressed air is supplied after the knockout starts and a gap is formed between the portion near the opening end and the die, the compressed air leaks out such that the bowl bottom cannot be flexed.
According to the twenty-fifth embodiment of the invention, since the supply of compressed air is initiated prior to the knockout, the undercut form portion can reliably be flexed.
Either female die or male die may be used. In the case of the male die forming the bowl, the softened thermoplastic resin plate is sucked to the outer surface of the die. When compressed air is supplied during the die-releasing, the bowl bottom is expanded outward to be flexed, so that the bowl bottom can easily be removed from the undercut forming portion.
Thus, the technique for assisting the die-releasing by flexing the molding immediately before the die-releasing is realized by a solid apparatus and in this sense, it can readily be understood that the invention may be applied to a solid apparatus. From the viewpoint that flexing by the supply of compressed air enhances the die-releasing, the twenty-sixth embodiment of the invention is a thermoforming female die formed into a bowl-shaped recess, and having vacuum and die-releasing holes concentrically formed in a bowl bottom and a hole communicating with atmosphere and formed in the vicinity of an open end.
In the twenty-sixth embodiment of the invention thus constructed, the vacuum and die releasing holes are disposed concentrically in the bowl bottom formed in the bowl-shaped recess. When the compressed air is supplied through the vacuum and die-releasing holes, the bowl bottom is flexed. Further, since the hole communicating with the atmosphere is disposed in the portion near the opening end, air present between the bowl bottom and the inner circumferential surface of the die is discharged into the atmosphere outside the die even if the air cannot be exhausted from the vacuum and die-releasing holes.
Of course, the invention may include the arrangement for control of air supply and exhaust. As one example, a twenty-seventh embodiment of the invention is constructed so that in the thermoforming female die of the twenty-sixth embodiment of the invention, the die further comprises a die-releasing compressed air supplying mechanism supplying compressed air through the vacuum and die-releasing holes so that a bowl bottom of the product is inwardly flexed in the die.
According to the invention of the twenty-sixth or twenty-seventh embodiment of the invention, the thermoforming female die wherein the die can easily be held can be provided.
The bowl bottom is flexed when the die-releasing compressed air supplying mechanism supplies compressed air from the vacuum and die-releasing holes. Flexing the bowl bottom assists the die-releasing irrespective of the presence of the undercut. The flexing is most effective when the undercut is formed. In view of this, a twenty-eighth embodiment of the invention is constructed so that in the thermoforming female die of the twenty-sixth or twenty-seventh embodiment of the invention, the die further comprises an undercut forming portion formed to spread out from the bowl bottom of the bowl-shaped recess, wherein compressed air is supplied through the vacuum and die releasing holes so that the bowl bottom of the product is flexed to be released from the undercut forming portion.
In the twenty-eighth embodiment of the invention thus constructed, the undercut forming portion is formed to be spread out from the bowl bottom of the bowl-shaped recess. When the molding is drawn in an ordinary manner, the undercut forming portion and the undercut of the molding interfere with each other. However, if the bowl bottom is inwardly flexed, the undercut of the molding becomes easy to pass through the undercut forming portion to thereby be removed therefrom.
According to the twenty-eighth embodiment of the invention, the spread-out undercut can be formed on the bowl bottom.
A sequence of operation is controlled by a sequencer when a molding with an undercut forming portion is thermoformed using the aforesaid thermoforming female die. In this case, the sequencer controls supply and exhaust of air through the vacuum and die-releasing holes, die releasing and knockout. Accordingly, the present invention may be applied to a control program for the above-described sequencer. Further, the invention may be applied to a medium on which the control program is recorded.
Of course, the recording medium may be a magnetic recording medium or photo magnetic recording medium. Further, the same idea may be adapted to any recording medium which is to be developed in the future. Moreover, it goes without saying that the same idea is adapted to a reproducing stage such as a primary reproduced product or secondary reproduced product. Besides, the present invention is also used in a case where the communication line is utilized as a supplying method.
Moreover, there is no difference in the concept of the invention in case where the invention is realized by partly a software and partly a hardware. It may be a type wherein a portion is stored on the recording medium to be suitably read as the need arises.